This invention pertains to cells for holding matter to be analyzed by spectrophotoanalysis, and more particularly to such cells which only require small volumes of material to be analyzed and provide high optical sensitivity. In addition, this invention has to do with such cells as designed for use in spectroelectrochemical analysis.
Spectroelectrochemistry is widely used for the study of the mechanisms and kinetics of electrode reactions as well as the characterization of electrogenerated species. The technique is frequently employed for the study of biological redox systems, including multicomponent systems. In such applications, it is frequently essential that the consumption of precious enzymes be minimized by employing cells which feature low volume and high optical sensitivity. These characteristics are also essential for the development of spectroelectrochemical systems for analytical applications.
Several approaches to the problem of minimizing sample volume have been pursued. These include miniaturized conventional cells, circulating cells, including multispectral and circulating long optical path (CLOSET) cells, optically transparent thin-layer electrode cells (OTTLE), and multiple specular reflectance (MSR) cells. All of these approaches have disadvantages. The miniaturized conventional and CLOSET cells have volumes of hundreds of microliters with relatively small surface area/volume ratios, and the samples therein must be stirred to achieve reasonable rates of electrolysis. Stirring may in some cases lead to denaturation of some delicate proteins. OTTLE cells require less volume than conventional or CLOSET cells, but the OTTLE cell has a very low optical sensitivity compared to conventional designs, and therefore requires much higher concentrations of chromophore to obtain comparable response, partially negating the advantage of low volume. Thus, the total quantity of enzyme required for an OTTLE cell may equal the quantity required for a much larger volume CLOSET cell which has greater optical sensitivity. The MSR cell is limited by the requirement for a laser source, and precise alignment of the optical elements. The OTTLE and MSR designs also suffer from the requirement for electrodes with specific optical properties, i.e., transparent (OTTLE) or reflective (MSR) electrodes.
Techniques have also been developed for kinetic studies in which a highly collimated beam is passed at a small angle or parallel to the electrode, using both laser and conventional continuum light sources. Considerable care is required in these techniques to collimate the continuum source. While the total solution volume in these techniques is quite large, the spectrally monitored region is confined to a small volume near the electrode surface and optical beam positioning is critical.